1、Unit 15 Temperature Sensors Unit 15 Temperature Sensors TextKey wordsTechnical termsExpressionsNotes to the textUnit 15 Temperature Sensors TextOne of the primary methods for electrical measurement of temperature involves changes in the electrical resistance of certain materials.In this,as well as o
2、ther cases,the principle measurement technique is to place the temperature-sensing device in contact with the environment whose temperature is to be measured.The sensing device then takes on the temperature of the environment.Thus a measure of its resistance indicates the temperature of the device a
3、nd the environment must wait until the device comes into thermal equilibrium with the environment.The two basic devices used as the Resistance-Temperature Detector(RTD),Unit 15 Temperature Sensors based on the variation of metal resistance with temperature,and the thermistor,based on the variation o
4、f semiconductor resistance with temperature.There exists another dependence of electrical behavior of materials on temperature that forms the basis of a large percentage of all temperature measurement.This effect is characterized by a voltage-generating sensor in which an electromotive force(emf)is
5、produced that is proportional to temperature.Such an emf is found to be almost linear with temperature and very repeatable for constant materials.Devices that measure temperature on the basis of this thermoelectric principle are called thermocouples(TCs).Unit 15 Temperature Sensors Here well briefly
6、 discuss the characteristics of Resistance-Temperature Detector(RTD).A Resistance-Temperature Detector(RTD)is a temperature sensor that is based on the principles that metal resistance increasing with temperature.Metal used in these devices vary from platinum,which is very repeatable,quite sensitive
7、,and very expensive,to nickel,which is not quits as repeatable,more sensitive,and less expensive.Unit 15 Temperature Sensors Sensitivity An estimate of RTD sensitivity can be noted from typical values of a0,the linear fractional change in resistance with temperature.For platinum,this number is typic
8、ally on the order of 0.004/,and for nickel a typical value is 0.005/.Thus,with platinum,for example,a change of only 0.4 would be expected for a 100 RTD if the temperature is changed by 1.Usually,a specification will provide calibration information either as a graph of resistance versus temperature
9、or as a table of values from which the sensitivity can be determined.For the same materials,however,this number is relatively constant because it is a function of resistivity.Unit 15 Temperature Sensors Response Time In general,RTD has a response time of 0.5 to 5 s or more.The slowness of response i
10、s due principally to the slowness of thermal conductivity in bringing the device into thermal equilibrium with its environment.Construction A RTD,of course,is simply a length of wire whose resistance is to be monitored as a function of temperature.The construction is typically such that the wire is
11、wound on a form(in a coil)to achieve small size and improve thermal conductivity to decrease response time.In many cases,the coil is protective tube that inevitably increases response time but may be necessary in hostile environments.A loosely applied standard sets the resistance at multiples of 100
12、 for a temperature of 0.Unit 15 Temperature Sensors Range The effective range of RTDs depends principally on the type of wire used as the active element.Thus,a typical platinum RTD may have a range of 100 to 650,whereas a RTD constructed from nickel might typically have a specified range of 180 to 3
13、00.Unit 15 Temperature Sensors Key wordssensor n.传感器thermal adj.热的，热量的equilibrium n.平衡，平静，均衡detector n.探测器，检波器，检电器thermistor n.热敏电阻thermoelectric adj.热电的electromotive adj.电动的thermocouple n.物 热电偶platinum n.白金，铂nickel n.化镍Unit 15 Temperature Sensors repeatable adj.可重复的sensitivity n.敏感，灵敏(度)，灵敏性fractio
14、nal adj.部分的calibration n.标度，刻度，校准graph n.图表，曲线图versus prep.与相对resistivity n.抵抗力，电阻系数conductivity n.传导性，传导率inevitably adv.不可避免hostile adj.敌对的，敌方的Unit 15 Temperature Sensors Technical termstemperature-sensing device 温度敏感器件thermal equilibrium 热量平衡Resistance-Temperature Detector(RTD)电阻温度计voltage-generat
15、ing sensor 产生电压的传感器electromotive force(emf)电动势the active element 有源元件Unit 15 Temperature Sensors Expressionsin contact with 与相关，联系come into 达到，得到based on 基于a large percentage of 很大的百分比be linear with与成线性on the basis of以为基础Unit 15 Temperature Sensors Notes to the text1.In this,as well as other cases,t
16、he principle measurement technique is to place the temperature-sensing device in contact with the environment whose temperature is to be measured.无论何种测量，其测量技术的原理都是将温度传感装无论何种测量，其测量技术的原理都是将温度传感装置与被测温的环境相接触。置与被测温的环境相接触。句中，“to place the temperature-sensing device”至句末的不定式用作表语；“whose temperature is to be
17、measured”为定语从句，修饰“environment”；“to be measured”是从句中的不定式作表语成分。Unit 15 Temperature Sensors 2.The two basic devices used as the Resistance-Temperature Detector(RTD),based on the variation of metal resistance with temperature,and the thermistor,based on the variation of semiconductor resistance with tem
18、perature.使用的两个测温器件分别是电阻温度计和热敏电阻，使用的两个测温器件分别是电阻温度计和热敏电阻，其中前者是金属电阻随温度变化而变化，后者是半导体电其中前者是金属电阻随温度变化而变化，后者是半导体电阻随温度变化而变化。阻随温度变化而变化。句中的“based on the variation of metal resistance with temperature”修饰“the Resistance-Temperature Detector(RTD)”；“based on the variation of semiconductor resistance with temperatu
19、re”修饰“the thermistor”；“the Resistance-Temperature Detector”和“the thermistor”相并列。Unit 15 Temperature Sensors 3.Metal used in these devices vary from platinum,which is very repeatable,quite sensitive,and very expensive,to nickel,which is not quits as repeatable,more sensitive,and less expensive.测温装置使用不同的金属制成，可以是重复性好、灵测温装置使用不同的金属制成，可以是重复性好、灵敏度高、价格高的铂，也可以是重复性不太好，但灵敏度敏度高、价格高的铂，也可以是重复性不太好，但灵敏度更高、价格较低的镍。更高、价格较低的镍。句中的“which is very repeatable,quite sensitive,and very expensive”修饰“platinum”；“which is not quits as repeatable,more sensitive,and less expensive”修饰“nickel”。
